Replacement
Replacing costs more than building new: the old system has to come out, crews work around an occupied home, and the new design must meet today's code — not the code your old system was built under.
Most failures are the drainfield. A cracked or collapsed tank is rarer.
A tank-only replacement typically runs $3,500 to $9,500: the new tank itself, pumping and crushing the old one in place or hauling it out, excavation, reconnecting inlet and outlet lines, and a permit with inspection. Concrete tanks cost more to remove than plastic. If the drainfield is healthy, nothing else changes.
This is the expensive one — usually $7,000 to $22,000, and more where soil forces a mound or aerobic system. A failed field cannot be repaired once the soil surface has sealed with solids; it is abandoned and a new field is built in the reserve area. If your permit never set aside a reserve area, a new soil evaluation decides what is possible, and that uncertainty is why quotes vary so widely.
Everything: new tank, new field, old-system decommissioning, and a fresh permit. Expect $12,000 to $35,000 depending on soil and state, at the top of that range where a conventional field is no longer permitted on your soil and an engineered system takes its place.
Sewage surfacing over the field, backups that return after pumping, and persistently saturated ground point to a failed field. But rule out the cheap causes first: a tank overdue for pumping, a clogged effluent filter, or a settled distribution box produce identical symptoms and cost a few hundred dollars, not twenty thousand. Insist on a proper inspection before accepting a replacement quote.